Atopic dermatitis has been defined by the American College of Veterinary Dermatology task force as “a genetically-predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features” (Olivry, et al. Veterinary Immunology and Immunopathology 2001; 81: 143-146). The task force also recognized that the disease in canines has been associated with allergen-specific IgE (Olivry, et al. 2001 supra; Marsella & Olivry Clinics in Dermatology 2003; 21: 122-133). Severe pruritus, along with secondary alopecia and erythema, are the most noticeable and concerning symptoms to pet owners.
The prevalence of atopic dermatitis is not known with precision due to poor and inconsistent epidemiological data, but is estimated to be 10% of the total canine population (Marsella & Olivry 2003 supra; Scott, et al. Canadian Veterinary Journal 2002; 43: 601-603; Hillier Veterinary Immunology and Immunopathology 2001; 81: 147-151). Globally, about 4.5 million dogs are affected with this chronic and lifelong condition. Incidence appears to be increasing. Breed and sex predilections have been suspected, but may vary greatly depending on geographical region (Hillier, 2001 supra; Picco, et al. Vet Dermatol. 2008; 19: 150-155).
The potential factors involved in allergic dermatitis are numerous and poorly understood. Components in food may trigger atopic dermatitis (Picco, 2008 supra), as well as environmental allergens such as fleas, dust mites, ragweed, plant extracts, etc. Genetic factors also play an important role. Although there is no confirmed breed predilection, some mode of inheritance is thought to increase predisposition to atopic dermatitis (Sousa & Marsella Veterinary Immunology and Immunopathology 2001; 81: 153-157; Schwartzman, et al. Clin. Exp. Immunol. 1971; 9: 549-569.
Interleukin-31 (IL-31) is a cytokine that was cloned in 2004. It is mainly produced by activated T helper (Th)2 cells (Dillon et al. Nat Immunol 2004; 5:752-60), but is also produced in mast cells and macrophages. IL-31 binds a co-receptor composed of IL-31 receptor A (IL-31RA) and the oncostatin M receptor (OSMR) (Dillon et al. 2004 supra and Bilsborough et al. J Allergy Clin Immunol. 2006 117(2):418-25). Receptor activation results in phosphorylation of STAT through JAK receptor(s). Expression of the co-receptor has been shown in macrophages, keratinocytes and in dorsal root ganglia. Recently, it has been found that IL-31 is involved in dermatitis, pruritic skin lesions, allergy and airway hypersensitivity. See FIG. 1.
Stimulation of T cells with anti-CD3 and anti-CD28 antibodies immediately upregulates IL-31 mRNA expression (Dillon et al. 2004 supra). Microarray analysis has shown that IL-31 induces certain chemotactic genes, such as CXCL1, CLL17 (thymus and activation-regulated chemokine [TARC]), CCL19 (macrophage inflammatory protein [MIP]3β), CCL22 (monocyte-derived chemokine [MDC], CCL23 (MIP3), and CCL4 (MIPβ) (Dillon et al. 2004 supra).
Transgenic mice that over-express IL-31 show skin inflammation, pruritis, severe dermatitis, and alopecia (Dillon et al. 2004 supra). Subcutaneous injection of IL-31 into mice triggers infiltration by the inflammatory cells, neutrophils, eosinophils, lymphocytes, and macrophages, and results in epidermal thickening and dermal acanthosis. In NC/Nga mice, with atopic dermatitis (AD) due to natural causes, IL-31 is overexpressed in skin lesions and correlates with pruritus (Takaoka et al. Eur J. Pharmacol. 2005; 516, 180-181; Takaoka et al. Exp. Dermatol. 2006; 15, 161-167). Also, in murine models, IL-31 has been shown to induce rapid onset pruritus (Raap et al. J Allergy Clin Immunol. 2008; 122(2):421-3)
Further studies have indicated that IL-31 is associated with atopic-dermatitis-induced skin inflammation and pruritus in humans. In human AD patients, the expression of IL-31 mRNA is considerably higher in skin lesions than in non-lesional skin, and the expression in non-lesional skin is greater than that in normal skin from healthy patients (Sonkoly et al. J Allergy Clin Immunol 2006; 117:411-7). Another study has reported that CD45RO+ (memory) cutaneous lymphocyte antigen (CLA)-positive T cells in the skin of AD patients express IL-31 mRNA and protein (Bilsborough et al. 2006 supra). It has also been reported that IL-31 mRNA overexpression in the skin of patients or allergic contact dermatitis is correlated with IL-4 and IL-13 mRNA expression, but not with interferon (IFN)-γ mRNA expression (Neis et al. J. Allergy Clin. Immunol. 2006; 118, 930-937). Furthermore, IL-31 serum levels have been shown to be elevated in human patients with chronic spontaneous urticaria and even more so in patients with AD (Raap et al. Exp Dermatol. 2010; 19(5):464-6). Also, a correlation of the severity of AD with serum IL-31 levels has been observed in humans (Rapp et al. 2008 supra). IL-31 secretion has also been shown to be enhanced in mast cells following IgE cross-linking and as a response to Staphylococcal superantigen in atopic individuals. In addition, IL-31 has been shown to stimulate the production of several pro-inflammatory mediators including IL-6, IL-8, CXCL1, CC17 and multiple metalloproteinases in human colonic myofibroblasts (Yagi, et al. International Journal of Molecular Medicine 2007; 19(6): 941-946.
Type I hypersensitivity against environmental allergens is considered to be the main mechanism of canine AD, and the levels of Th2-mediated cytokines, such as IL-4 are increased in the skin lesions of dogs with AD (Nuttall, et al. Vet. Immunol. Immunopathol. 2002; 87, 379-384). Moreover, infiltration by inflammatory cells, lymphocytes and neutrophils, is an important mechanism underlying the aggravation of the skin lesions; the overexpression of chemotactic genes such as CCL17/TARC, CCR4, and CCL28/mucosae-associated epithelial chemokine (MEC) contributes to the aggravation of skin lesions in the dogs with AD (see, Maeda, et al. Vet. Immunol. Immunopathol. 2005; 103, 83-92; Maeda, et al. Vet. Immunol. Immunopathol. 2002b; 90, 145-154; and Maeda, et al. J. Vet. Med. Sci. 2008; 70, 51-55).
Recent evidence has suggested that IL-31 might be involved in promoting allergic inflammation and an airway epithelial response characteristic of allergic asthma (Chattopadhyay, et al. J Biol Chem 2007; 282:3014-26; and Wai, et al. Immunology, 2007; 122, 532-541).
These observations support the hypothesis that IL-31 plays a significant role in both pruritic and allergic conditions. It would be desirable to provide a therapeutic antibody against IL-31 useful for treating a pruritic condition and/or an allergic condition in dogs or cats.